Materials have been separated into selected different sizes for a variety of purposes for many, many years. To accomplish the separation, numerous devices and machines have been developed from the very simple to the very complex, depending upon the particular use and the materials to be separated. The prior art devices and machines range from a simple box with a screen wire bottom to very expensive shaker decks or trommels. All of these devices and machines use a screen medium of a specific size and shape which will allow particles smaller than the openings to pass through while the larger particles are retained on the screen, and a suitable method of collecting the various sizes in separate locations is usually combined with the separating device itself. Also, some prior art systems combine one or more screens into a more complex apparatus, so as to separate materials into two or size ranges as the materials passes through the apparatus.
Most prior art devices have a separation screen that is shaped into a cylinder and revolved about an inclined axis. Examples of such revolving screens are shown in Hanna U.S. Pat. No. 928,965 and Dietert U.S. Pat. No. 3,208,593. More complex separating apparatus may add some means for increasing the screening effect, such as an agitator or vibrator. Fulghum, Jr. et al, U.S. Pat. No. 4,140,281 shows a revolving cylindrical screen with an added means for initially separating particles in a specialized application. Other known prior art separators teach banks of flat screens each mounted on an incline with vibrators added to each screen.
An example of a separating apparatus that does not utilize screens but a plurality of revolving disks of different diameters mounted on an inclined axis is shown in Hering U.S. Pat. No. 1,216,118.
The known prior art devices and machines are quite effective when the material to be separated is heavy, firm, granular and dry. However, a variety of waste recovery processes have been developed in recent years which have created a need for a screening method and apparatus that will work effectively and efficiently with difficult materials which are soft, wet, sticky, and may contain lightweight or other foreign materials such as plastic film, or paper particles. Such materials are difficult to efficiently separate, and conventional screens do not perform well since they usually become plugged or blinded. This requires frequent shutdown for manual cleaning or costly equipment to continuously clean the screen medium.
There is therefore a need for an apparatus for separating materials which may contain soft, wet, sticky, or a variety of foreign materials that include lightweight, plastic, and paper particles.
There is a further need for an apparatus for separating these difficult materials efficiently and at a low cost to make the screening apparatus available for a variety of different uses by a variety of different users who conduct both small and large operations.